Ultrawideband (UWB) is a recent technology that brings attractive solutions for future wireless broadband applications. Impulse Radio (IR) is a popular implementation of UWB systems; although conceptually not very new, UWB-IR is recently becoming popular for wireless communications. It is realized by the transmission of extremely short duration (usually sub-nanosecond) pulses.
A major challenge when designing UWB systems is the selection of the appropriate data mapping format. Depending on the parameters such as design specifications and constraints, range, transmission and reception power, quality of service requirements, regulatory requirements, and hardware complexity, there may be different modulation options that will satisfy the system designer under different scenarios. One of the popular modulation options is pulse position modulation (PPM), where the position of the transmitted pulse is varied depending on the information bits. One of the attractive features of the PPM modulation in UWB is that it allows the use of non-coherent detection at the receiver, avoiding the complex and difficult channel estimation process.
In wireless communications, the transmitted UWB signals that propagate through a radio channel are typically reflected, diffracted, and scattered, arriving at the receiver through multiple paths. In UWB, the resolvable multipath components are much larger, typically on the order of a hundred. The multipath propagation causes cross-modulation interference (CMI) for PPM modulated signals if the time difference between two possible hopping positions (i.e. modulation index) is less than the maximum excess delay of the channel. CMI degrades the performance of the UWB receiver.
CMI has been studied extensively for various UWB receiver architectures, and it has been shown that CMI has a major impact in the receiver performance. It is suggested strongly that solutions to avoid/suppress CMI are needed to improve the performance of PPM modulated UWB signals. The effect of CMI on average BER performance of UWB receivers has been studied and it has been demonstrated that CMI significantly degrades the average BER performance of receivers. More significantly, CMI causes catastrophic errors when a strong multipath component occurs at the opposite symbol location. Therefore, average BER performance degradation does not tell the whole story. There are cases where the CMI interference can hurt the receiver so badly that it eventually causes a sequence of symbol errors and hence shuts down the communication link completely.
Increasing the transmitter power may not even help in these cases. This motivates the need for techniques to suppress CMI.
Accordingly, what is needed in the art is a system and method for an improved cross-modulation interference (CMI) reduction technique for pulse-position modulated UWB signals.